Tree - soil interactions depend on environmental conditions. Planting trees may affect soil microbial communities and compromise their functioning, particularly in unfavorable environments. To understand the effects of tree species composition on soil microbial communities, we quantified structural and functional responses of soil microorganisms to tree species planted in various environments using substrate-induced respiration and phospholipid fatty acid analyses. Five forest types were studied including pure stands of native European beech (Fagus sylvatica), range expanding Norway spruce (Picea abies), and non-native Douglas-fir (Pseudotsuga menziesii), as well as the two conifer - beech mixtures. We found that microbial functioning depends strongly on soil nutrient concentrations in the studied forest sites. At nutrient-poor sites, soil microorganisms were more stressed in pure and mixed coniferous forests, especially in Douglas-fir, compared to beech forests. By contrast, microbial structure and functional indicators in beech forests varied little with site conditions, likely because beech provided ample amounts of root-derived resources for microbial growth. Since soil microbial communities are sensitive to Douglas-fir, planting Douglas-fir may compromise ecosystem functioning, especially at nutrient-poor sites. Overall, root-derived resources are important for determining the structure and functioning of soil microbial communities, so soil microbial responses to tree species will depend upon the provisioning of these resources as well as site-specific environmental conditions.

树与土壤的相互作用取决于环境条件。种植树木可能会影响土壤微生物群落并损害其功能，特别是在不利的环境中。为了了解树木物种组成对土壤微生物群落的影响，我们使用底物诱导的呼吸作用和磷脂脂肪酸分析，定量了土壤微生物对各种环境中种植的树木物种的结构和功能响应。研究了五种森林类型，包括纯天然欧洲山毛榉（Fabus sylvatica），扩大范围的挪威云杉（Picea abies）和非本地花旗松（Pseudotsuga menziesii）），以及两种针叶树-山毛榉的混合物。我们发现，微生物功能在很大程度上取决于所研究森林中土壤养分的浓度。与山毛榉森林相比，在营养贫乏的地区，纯净和混合针叶林，尤其是花旗松中的土壤微生物承受的压力更大。相比之下，山毛榉森林中的微生物结构和功能指标随场所条件变化不大，这很可能是因为山毛榉为微生物的生长提供了大量的根系资源。由于土壤微生物群落对花旗松很敏感，因此种植花旗松可能会损害生态系统的功能，尤其是在营养缺乏的地区。总体而言，根源资源对于确定土壤微生物群落的结构和功能非常重要，